Molding Composition

This invention relates to improved molding compositions.

More specifically, this invention relates to interpolymers resulting from the polymerization of a vinyl/aromatic monomer such as styrene, an olefinic nitrile such as acrylonitrile and a maleimide in the presence of both an ethylene-propylene-diene terpolymer (EDPM) and an ethylene based thermoplastic elastomer containing an acrylate functionality and to molded products produced therefrom.

The use of EPDM rubbers for impact modification has been demonstrated for polystyrene in blends with polyphenylene oxide as described in U.S. Pat. Nos. 3,658,945; 3,943,191 and 4,152,316. Moreover, the use of EPDM rubbers to impact modify styrene/maleimide/acrylonitrile terpolymers is taught in Canadian Pat. No. 1,079,893. It is also well known to employ EPDM to impact modify styrene/acrylonitrile copolymers. See for example U.S. Pat. Nos. 3,489,822; 4,166,881 and 4,202,948.

The present invention provides a novel thermoplastic molding composition which utilizes an ethylene based thermoplastic elastomer containing an acrylate functionality in combination with an EPDM rubber to improve at least one property of the molded thermoplastic composition. The incorporation of the ethylene based thermoplastic elastomer containing an acrylate functionality has, quite surprisingly, been found to significantly improve the impact strength of the molded composition through a proportionate degree of miscibility between the matrix resin and the acrylate functionality on the ethylene based thermoplastic elastomer.

According to this invention, there is provided a thermoplastic molding composition comprising: (a) a matrix resin comprised of a monoalkenyl aromatic monomer, a dicarboxylic anhydride imide and a monoalkenyl nitrile monomer; (b) an EPDM rubber; and (c) an ethylene based thermoplastic elastomer containing an acrylate functionality wherein the molding composition is produced by polymerizing the matrix resin (a) in the presence of (b) and (c).

Also, according to this invention there is provided a method for producing a moldable compound which comprises incorporating an EPDM rubber and an ethylene based thermoplastic elastomer containing an acrylate functionality into a matrix resin composition comprised of a monoalkenyl aromatic monomer, a dicarboxylix anhydride imide and a monoalkenyl nitrile monomer; and, polymerizing the resulting composition, the ethylene based thermoplastic elastomer being present in an amount sufficient to improve at least one property of the molded composition.

In its preferred embodiment the thermoplastic molding composition of this invention will comprise in weight percent (a) from about 65 to about 95 of a matrix resin comprised of from about 40 to about 75 of a monoalkenyl aromatic monomer, from about 20 to about 35 of a dicarboxylic anhydride imide and from about 5 to about 25 of a monoalkenyl nitrile monomer; (b) from about 3 to about 25 EPDM rubber; and (c) from about 2 to about 10 ethylene based thermoplastic elastomer containing an acrylate functionality.

Any suitable monoalkenyl aromatic monomer can be employed to produce the matrix resin. Suitable monoalkenyl aromatic monomers include styrene, alpha-methylstyrene, para-methylstyrene, t-butylstyrene or any mono-, di-, or trihalogenated styrene, and the like, and their mixtures.

Any suitable dicarboxylic anhydride imide can be employed to produce the matrix resin. Suitable dicarboxylic anhydride imides include maleimide, N-methylmaleimide, N-ethylmaleimide, N-phenylmaleimide or any N-(mono-, di-, or trihalogenated)phenylmaleimide, and the like, and their mixtures.

Any suitable monoalkenyl nitrile monomer can be employed to produce the matrix resin. Suitable monoalkenyl nitrile monomers include acrylonitrile, methacrylonitrile, and their mixtures. The monoalkenyl nitrile monomer employed in the matrix resin is preferably acrylonitrile.

The ethylene based thermoplastic elastomer will comprise from about 99 to about 75 weight percent ethylene and from about 1 to about 25 weight percent of a monoalkenyl acrylate. The monoalkenyl acrylate can be selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, and the like, and their mixtures. The most preferred monoalkenyl acrylate is ethyl acrylate.

The EPDM rubber is comprised of ethylene, propylene and a nonconjugated diene such as 1,4-hexadiene, dicyclopentadiene or most preferably, ethylidene norbornene.

The molecular weight of the matrix resin should be between about 100,000 to about 700,000; most preferably about 200,000 to about 500,000. The EPDM rubber should possess a molecular weight of about 100,000 to about 500,000; most preferably about 200,000 to about 400,000.

The thermoplastic molding composition of this invention is most conveniently prepared in a solvent or solvent mixture. Useful solvents are benzene, toluene, chlorobenzene, xylene, hexane, heptane and the like, and their mixtures. Particularly suitable for use is a solvent mixture comprised of 40 to 60 weight percent of chlorobenzene and 60 to 40 weight percent of heptane. The EPDM rubber and ethylene based thermoplastic elastomer are dissolved in the solvent mixture typically at ambient temperature. The polymerization of matrix resin monomers in the presence of the EPDM rubber and the ethylene based thermoplastic elastomer is conducted at a temperature within the range of from about 60.degree. C. to about 120.degree. C., most preferably between 70.degree. C. and 90.degree. C. The free radical initiators which are useful are benzoyl peroxide, t-butyl perpivalate, t-butyl peracetate, t-butyl peroctoate and t-butyl perbenzoate. Benzoyl peroxide is the preferred initiator.

Prior to any type of thermal processing, the polymer is stabilized. Any of the commercially available antioxidants are acceptable, however, most preferred is an equal weight percent mixture of N,N-diphenylp-phenylene diamine and tris(mono- and dinonyl)phenyl phosphite totaling between about 1 to about 2 weight percent.

Evaluation of material properties was performed based on the following ASTM standard tests: flexural strength and modulus (D-790), tensile strength (D-638), notched Izod (D-256) and DTUL (deflection temperature under load, D-648). Gardner Falling Weight Index was established using a 1/2" diameter eight-pound weight and a 11/4" diameter orifice. Glass transition temperature was evaluated by differential scanning calorimetry. Melt Flow parameters were established via melt indexing.

The invention is demonstrated by the following examples.

This example demonstrates the preparation of a molding composition of this invention.

A 4-liter reactor was charged with a solvent mixture of 300 g of monochlorobenzene and 300 g of heptane. About 39 g of EPDM Rubber (Polysar.RTM.585; 10% ethylidene norbornene, Mooney viscosity ML 1+4 212.degree. F.) and 6 g of ethylene-ethyl acrylate (18% ethyl acrylate) were dissolved in the solvent mixture at ambient temperature. The internal temperature of the reactor was raised to 75.degree. C. A solution of 94 g of styrene, 60 g N-phenylmaleimide and 20 g acrylonitrile containing 1.5 g of benzoyl peroxide was added to the reactor. The stirring rate was 60 rpm. After two hours, the reactor was brought to 80.degree. C. and a second portion of initiator, 1.0 g benzoyl peroxide was added. Four hours from the start of the reaction, 300 g of a 50:50 co-solvent mixture (chlorobenzene:heptane) were added. Total reaction time was seven hours, and was followed by devolatilization at 170.degree. C. under vacuum. The reaction product was recovered, converted into grinds and extruded at 270.degree. C. Samples for testing were prepared by injection molding at 280.degree. C. Prior to processing, the grinds were stabilized with 1 weight percent of a 50:50 mixture of N,N-diphenyl-p-phenylene diamine and tris(mono- and dinonyl) phenyl phosphite. The molding composition and its properties are outlined in Table I.

The molding composition of Example I was further tested and found to exhibit good thermal stability in an oxygen atmosphere. The composition exhibited a 1% and a 5% weight loss in an oxygen atmosphere at 302.degree. C. and 347.degree. C., respectively.

This example serves to demonstrate the miscibility between the styrene/N-phenyl maleimide/acrylonitrile resin (S/N-PMI/AN) matrix and the acrylate functionality in the ethylene based thermolastic elastomer.

The S/N-PMI/AN-EPDM tested in Compositions Nos. 1-4 was prepared using substantially the procedure of Example 1 and employing the same ingredients and amounts except that the 6 g of ethylene-ethyl acrylate were replaced with an additional 6 g of EPDM. For the purpose of glass transition determination composition Nos. 2, 3 and 4 were prepared by melt blending the specified amounts of S/N-PMI/AN-EPDM and ethylene-ethyl acrylate.

The ethylene-ethyl acrylate comprised 18% ethyl acrylate and 82% ethylene. The glass transition reported refers to the S/N-PMI/AN resin matrix only.

This example serves to demonstrate the flexibility of the matrix composition to include a halogenated monoalkenyl aromatic monomer for the purpose of flame retardancy.

The process, as outlined in Example 1, was followed identically except that the monoalkenyl aromatic monomer feed to the reactor comprised 83 g styrene and 11 g of dibromostyrene. Table II defines the matrix composition and resin properties for a fire retardant resin in which 12.2 g of antimony oxide (Sb.sub.2 O.sub.3) was melt compounded with 203 g of resin prior to molding test specimens.

This example serves to demonstrate the improvement obtained by the utilization of the dual rubber (EPDM-ethylene based thermoplastic elastomer) system of this invention as compared to the employment of EPDM rubber alone.

Example 1 was followed identically except the 6 g of ethylene-ethyl acrylate were replaced with an additional 6 g of EPDM (Polysar.RTM.585). The overall weight % of rubber-ethylene thermoplastic elastomer in the matrix resin described in Example 1 was 22%; the overall weight percent of rubber in the resin obtained in this example was 22%. Properties for the all EPDM containing resin (not according to this Invention) are outlined in Table III and compared with the properties for the dual rubber containing composition of this invention, prepared in Example I.

The above data serve to illustrate that the molded compositions of this invention containing a dual rubber combination of an EPDM rubber and ethylene based thermoplastic elastomer exhibit at least one improved property as compared to a similar composition comprising only EPDM rubber. The molded composition of this invention, for example, exhibited a 66% improvement in the notched Izod test and a 100% improvement in the Gardner Falling Weight Index test. Elongation and Melt Index property valves also showed noticeable improvement.

It is evident from the foregoing that various modifications can be made to this invention. Such, however, are considered as being within the scope of this invention.